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Old 03-28-2007, 09:29 AM
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Default surging idle

I just finished doing a top-end job on my daughter's 94 Accord EC 2.2 Vtec. Everything went pretty well thanks to all the great info on this forum. It started right up and runs fantastic, with one slight has the dreaded surging idle problem, up and down between 1000 and 1500 rpm. It's OK when dead cold and then it starts doing it after it warms up a little. The interesting thing, and I think it might point to what is wrong, is thatwhen the cooling fan kicks on, the surging stops and it idles perfectly. As soon as the fan stops, the surging returns. It makes me think that it is related to a temp sensor somewhere. I already removed the IAC valve and cleaned it and replaced the dual seemed to help a little by reducing the amount of surging, but the overall problem remains. Does this ring a bell with anyone??
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Old 03-28-2007, 12:02 PM
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Default RE: surging idle

Did you adjust your base idle? It sounds like your IACV is operating too close to the 'closed' end of it's control range. That's caused by the base idle being set too high.

Firsteliminate anyvacuum leaks and make sure there's no air pockets in the cooling system.

Warm it up completely. Turn off all electrical loads.
Unplug the IACV - idle speed should drop low, almost stalling.
Use the idle air bypass screw to adjust idle to *600?? rpm.
(radiator fan's electrical load will mess this up, so adjust when it's not running)
Turn off the engine. Plug IACV back in. Reset ECU. Cool down.
Start engine without touching gas pedal.
Let it idle to warm up without touching gas pedal.

**check a repair manual for your year/version - some are 500 rpm.
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Old 03-28-2007, 10:44 PM
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Default RE: surging idle

Jim: Thanks for the help.....I adjusted the idle as low as it would go...the emissions sticker said it should be 750 rpm. With the idle screw turned all the way in, it would only drop to about 900 rpm. I reset the ECU and the surging idle is idles smoothly, but itstill idles a little high. Should the idle be that high with the bypass screw turned all the way in? In the old days the car would stall out if the bypass screw was turned all the way there something else I need to look at?
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Old 03-28-2007, 11:37 PM
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Default RE: surging idle

You have an intake air leak somewhere. Try spraying w/ a can of throttle body cleaner to help locate the leak. When cleaner is pulled into the leak, the idle will change. Check around all seams of throttle body and intake manifold.

good luck
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Old 03-29-2007, 01:03 AM
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Default RE: surging idle

Sounds like you have a vacuum leak somewhere. Fix it first, otherwise this other stuff isn't gonna work properly. If you unplug the IACV & turn the idle screw all the way in, it SHOULD stall. Here's a couple more things for you to check out.

There's also another valve underneath the throttlebody. The fast-idle thermo valve (FITV) will open when cold, and close itself as the engine warms up. It's job is to provide the fast-idle when you first start a cold engine. I think there's a DIY procedure around here somewhere. There's a plunger inside the FITV that can come loose. Screw it back into place...

Possibly the mechanical stop adjustment on the throttle itself? There's a stop somewhere on the throttle cable drum. Some people use that in a misguided attempt to adjust their idle. But that thing is supposed to just barely hold the throttle, only enough to prevent it from wedging stuck in the bore.

The sticker under the hoodhas the operatng idle, with the IACV plugged in and operating. That's not what you adjust to. The "BASE" idle is a lower RPM that you set while the IACV is unplugged. It's generally a couple hundred rpm lower than the normal operating idle.

ps... here's a test:
Warm it up thoroughly, let it idle, & unplug the IACV.
There's 2 small holes in the throttlebody bore, I think on the left as you're looking into the bore. They're for the IACV and the FITV. When the IACV is unplugged, it should not draw any air. Since it's warm, the FITV also should not draw any air. If those holes have suction, that's your problem. Cover them with your finger & see if the engine stalls.
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